1. Field of the Invention
The present invention relates to a device for loading and unloading a workpiece into and from a vacuum chamber which is used for semiconductor production and the like. More particularly, the present invention relates to a loading device for a vacuum chamber in which dust contamination of workpieces must be strictly avoided.
2. Description of the Related Art
Vacuum chambers are widely used for chemical and physical processing, such as evaporation, sputtering, ion plating, etching, etc., of, for example, semiconductor materials. Recently developed VLSICs (Very Large Scale Integrated Circuits) require a sub-micron fabrication precision. However, the size of IC chips and the size of the wafers on which the ICs are fabricated are both becoming larger. Thus, the amount of dust contaminating the workpiece must be reduced because it directly affects the yield and quality of IC production. Therefore, reduction of the amount of dust within the atmosphere in which the workpiece is processed becomes an essential requirement to achieve high quality and an increased production yield of VLSICs.
There are several methods in which dust contamination of a workpiece in a vacuum occurs. The first method is contamination caused by dust which has already been deposited on the workpieces or tools, such as chip transfer devices, before they are input to the vacuum chamber. The second method is contamination caused by dust in the gas in the vacuum chamber before it is evacuated. The third method is contamination caused by dust previously deposited on various parts within the chamber that is blown about by a turbulent gas flow while gas is evacuated or introduced into the chamber.
There have been extensive efforts to reduce the dust in the processing atmosphere. Particularly, in order to overcome the above-described third contamination problem, loading and unloading chambers, (referred to hereinafter as loading chambers), have been used. Examples of loading chambers are shown in FIGS. 1 and 2. In FIGS. 1 and 2, a loading chamber 2, 2' or 4 is coupled to a processing chamber 1 where the workpiece is processed. The workpiece is moved in and out of the processing chamber through the loading chambers. The loading chambers 2, 2' or 4 are connected to the processing chamber 1 by gates 11 or 12 capable of being opened as well as vacuum-sealed. The system shown in FIG. 1 is provided with a vacuum chamber 2 used exclusively for loading workpieces into the processing chamber 1, and a vacuum chamber 2' used exclusively for unloading workpieces from the processing chamber 1. The system of FIG. 2 is provided with a single loading chamber 4 used for both loading and unloading workpieces. These two types of loading and unloading chamber systems are so-called load-lock systems.
With reference to FIGS. 1 and 2, the procedure for loading and unloading workpieces into or from the processing vacuum chamber 1 is as follows. A gate 21 of the loading chamber 2 (FIG. 1) or a gate 41 of the loading chamber 4 (FIG. 2) is opened. Workpieces are introduced through the opened gate 21 or 41 and placed in the loading chamber 2 or 4. The gate 21 or 41 is then closed and there is a several minute wait until the floating dust in the chamber 2 or 4 settles. Then, the loading chamber 2 or 4 is evacuated by a vacuum pump 23 or 43. The processing chamber 1 has been previously evacuated by a pump 14. Gate 11 is then opened and the workpiece is transferred into the processing chamber 1. When unloading workpieces from the processing chamber 1 in FIGS. 1 or 2, the loading chamber 2' or 4 is evacuated by a vacuum pump 33 or 43, respectively, and a gate 12 between the chamber 1 and 2' or a gate 11 between the chamber 1 and 4, is opened. The workpiece is transferred from the processing chamber 1 to the loading chamber 2' or 4 through the opened gate 12 or 11, respectively. After the gate 12 or 11 is closed, a gas introduction device 32 or 42 fills the chamber 2' or 4 with gas, and then gate 31 or 41 is opened to remove the workpiece from the loading chamber 2' or 4.
The above-mentioned gas introduced into the loading chambers 2, 2' and 4 is extensively filtered by a filtering device (not shown) to minimize the amount of dust contained therein. Inert gas, such as pure nitrogen, is generally used to avoid introduction of a chemically active gas which may harm the workpiece.
In the above-described prior art vacuum chamber system, including the loading chambers, during the evacuation cycle or gas introduction cycle for chamber 1, dust which is deposited on various parts of the chamber is blown up, but the workpiece is not in the processing chamber. When a workpiece is moved in or out of the processing chamber 1, the processing chamber is already evacuated and the floating dust has settled since dust cannot float in a vacuum. Therefore, there is no problem with dust in the processing vacuum chamber 1.
However, in the loading chamber 2, 2' or 4, during the evacuation cycle or gas introduction cycle, dust, already deposited on various parts of the loading chamber is blown about by a turbulent flow of gas and may settle on the workpiece. This type of contamination corresponds to the third contamination method, as described above, by which dust can contaminate a workpiece.
To reduce dust in the loading or unloading chamber, several other methods have been proposed. For example, provisional publication of Japanese Patent No., TOKUKAI 60-27114, Feb. 12, 1985, by Tsuchiya, discloses a method for reducing dust accumulated on surfaces of various portions within the chamber. This method includes a procedure of repeating gas introduction and evacuation cycles of the loading chamber before a workpiece is placed therein. Gas introduced into the chamber produces a turbulent flow which blows dust into the gas atmosphere of the chamber. By evacuating this gas, the floating dust in the gas is exhausted with the gas. Repetition of this cycle reduces the amount of dust within the chamber.
Though the prior art, as described above, is effective to some degree in reducing the amount of dust in the workpiece atmosphere, there still exists a need to reduce even more the amount of dust deposited on a workpiece to achieve better yields and better quality VLSIC production.